The negative correlation between prolactin and ionic calcium in cord blood of full term infants.

Total serum calcium (Ca), ionic calcium (Ca++), phosphorus, magnesium, total protein, immunoreactive parathyroid hormone (iPTH), calcitonin (iCT) and prolactin (iPRL) were measured in 30 paired samples of cord and maternal blood obtained at term delivery. In the cord blood, the concentrations of Ca, Ca++, phosphorus, magnesium, albumin, iCT and iPRL were all higher, and the concentrations of total protein and iPTH lower than in the maternal blood. The calcium binding capacity of albumin assessed with the equation (Ca-Ca++)/albumin, was similar at a given concentration of Ca in both the maternal and fetal circulations. There was a significant positive correlation between cord Ca++ and maternal Ca or Ca++, and a significant negative correlation between Ca++ and iPRL in cord blood. These data suggest that there is an active system transporting calcium from mother to fetus through the placenta, and PRL is the only one of the three hormones which was correlated with ionic calcium values in the fetus. The negative relationship between Ca++ and iPRL in the cord blood suggests an inhibitory effect of the relative hypercalcemia on PRL secretion in the fetus.